Which Solar Photovoltaic System To Use?

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Which Solar Photovoltaic System To Use? 
by Linda Pang

In Singapore, there are three main solar photovoltaic systems that are often used. but of the three, which PV system is better suited to the needs of a particular project? To answer this pertinent question, we embarked on an investigative comparative study of the PV systems for the Pasir Ris Sports & Recreation Centre project.

Project Background
The Pasir Ris Sports & Recreation Centre was recently celebrated as the 1,000th certified green building since the Building and Construction Authority’s (BCA) Green Mark Scheme was introduced in 2005. The project achieved the BCA Green Mark GoldPlus, the second highest rating under the green building rating scheme.

Designed with a “Sporting Sanctuary in the Park” concept, the Centre integrates tropical passive design, green features, as well as a seamless connection to the neighbouring town park to create a user-friendly and environmentally friendly building.

The centre has a few distinguishing green features. It is 25% more energy efficient than an average building without green features, and has an impressive 170kWp photovoltaic system on its rooftop, which is expected to generate about 207,380 kWh of electricity each year to support up to 12% of its annual energy consumption. This is equivalent to the amount of energy used to power up 43 four-room HDB flats, which will help the centre save about $57,000 annually (based on estimated tariff rate of $0.276/kWh). Another interesting feature is a human-powered exercise bicycle in the gym that allows users to generate electricity while working out. The electricity generated from the bicycle can be stored to power up the television in the gym for more than eight hours. An interactive public display system located at the foyer of the Centre allows visitors to learn more about the Centre’s green initiatives, as well as keep track of the building’s energy consumption. The building is fitted with water and energy efficient features such as LED lighting and incorporates passive design to enhance daylighting and natural ventilation in common areas. In addition, louvres acting as sunshading screens are installed on the building’s façade to prevent heat gain into the building. These timber louvres are recycled from the timber benches of the old National Stadium, helping to preserve our heritage as well as the environment.

How PV Works
Solar PV systems convert sunlight directly into electricity. This is different from solar thermal systems that trap heat to warm up water. When PV panels are exposed to sunlight, they generate direct current electricity (“DC”). An inverter then converts the DC into alternating current electricity (“AC”), so that it can feed into one of the building’s AC distribution boards without affecting the quality of the power supply.

Common PV Technologies
A solar PV system is powered by many crystalline or thin film PV modules. Individual PV cells are interconnected to form a PV module or panel, making it easier for installation.

PV cells are made of light-sensitive semiconductor materials that use photons to dislodge electrons to drive an electric current. There are two broad categories of technology used for PV cells, namely crystalline silicon, which accounts for the majority of PV cell production, and thin film, which is newer and growing in popularity. There are currently three main PV systems that are used in Singapore:
– Mono-crystalline
– Poly-crystalline
– Amorphous Thin Film

PV Selection Criteria
We took into consideration several selection criteria, such as efficiency, cost and reflective properties. Efficiency is defined as the proportion of sunlight that the PV cell converts to electrical energy. In hot climates, the temperature coefficient of power should be factored into efficiency calculations, because PV cell performance declines as cell temperature rises. PV modules are rated at a cell temperature of 250C, but in Singapore, where cell temperatures can reach over 700C, the loss in power output at 700C is measured as (70-25) x temperature coefficient. A lower coefficient is better for PV yield. Thin Film has a much lower temperature coefficient than Crystalline Silicon, therefore in effect, Thin Film is overall more efficient under high temperatures.

PV Location
Consideration was also given to the location of the PV panels that would optimise the output of the PV cells. Singapore is situated on the Equator, which means that PV panels are more suitable for flat roofs or sloped roofs. Steep roofs, facades and other vertical surfaces would not be suitable.

PV Comparison Table

Findings and Recommendations
Based on our findings that many criteria, including cost, are quite comparable, and that Thin Film is actually more efficient in Singapore’s hot climate with overcast skies, the project team felt that the criterion of panel reflectivity was a key deciding factor, given that the Centre is located close to many high-rise residential flats. If Crystalline PV panels were to be used, when the sun shines on 2,400 sqm of glazed panels placed on the roof, the PV panels would be like a huge mirror, causing glare problems to residents both near and far. This was ascertained to be a high probability and high risk scenario. Hence, it was a unanimous decision among the team members that Thin Film be recommended to the client as the most appropriate system to use.♦

Reference: Handbook for Solar Photovoltaic (PV) Systems by BCA and EMA
Project team members: Linda Pang, Jane Kung, Ng Kim Leong, Ng Cher Heong, Anand Parthasarathy

Disclaimer: While reasonable effort has been taken in the compilation of information in this article, the author assumes no responsibility or liability for any consequences (financial or otherwise) suffered directly or indirectly by persons who have entered into commercial activities or otherwise upon reliance on any information in this document.

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